Google has rolled out another feature designed, evidently, to help protect users from themselves: An "Undo Send" option for its Gmail service.

It's the latest in a series of Google's experimental Gmail Labs features that the company has been making available as options to users.

Gmail Labs' newest addition, Undo Send, differs significantly from the features in many e-mail clients that let you to "recall" or cancel e-mails that have already been sent. Instead, Undo Send is for that split second of regret you might experience after hitting the "send" button on, say, a colorful message you accidentally cc'd to your boss.

With Undo Send enabled, you get a brief pop-up when you clicking on Gmail's "Send" button: "Your message has been sent. Undo. View Messages." Clicking "Undo" cancels the sending process and brings you back to the original message.

But you have to be quick. The Undo pop-up only lasts five seconds, after which the message is automatically sent on its way.

It's the most recent case of a Gmail Labs feature offering a layer of protection to users before they do something stupid. Last year, the company debuted Gmail Goggles, a similar feature that kicks in during specified times (by default, on late weekend nights) to prevent a user from sending out an e-mail while under the influence.

Like other experiments in Google's Labs, Undo Send had been tested internally for months before being released publicly. Michael Leggett, a user experience designer at Google, said in a blog post that testing showed "even just five seconds would be enough time to catch most of those regrettable e-mails."

Any longer would be that much time spent waiting for e-mails to be sent -- which could prove irritating when most are perfectly fine.

And while five seconds is not a lot of time, Leggett noted that at least in those five seconds, "you have a chance to hit the panic button."

Undo Send is available under the Settings tab at the top of the Gmail page. After clicking Settings, users can click on the Labs tab to see a long list of Gmail Labs' optional features, like Undo Send, that can be turned on or turned back off.

Other experimental add-ons available to Gmail users include offline access to e-mail and YouTube, Picasa and Flickr previews from within Gmail.

Gmail will celebrate its fifth anniversary next month and has gained millions of users as it rolls out new features. But Google has given Gmail the distinction of being one of the longest-running services to still be in public beta-testing -- witness the "BETA" still prominently displayed on Gmail's launch screen.

That's not to say that Gmail has proven entirely problem-free yet. There have been some glitches with the offering in the recent past, including a few service outages.